1. Field of the Invention
The present invention generally relates to a motor controlling circuit of a reproducing apparatus and a method of controlling. More specifically, the present invention relates to a motor controlling circuit for controlling the rotational speed of a motor for driving a recording medium such as a digital audio disk responsive to a reproduced signal from the disk.
2. Description of the Prior Art
A recording medium such as an optical video disk has an FM modulating signal recorded on the surface of a disk made of vinyl chloride in an arrangement of pits in a spiral manner, for example. A disk of this type may be utilized as a PCM disk or a digital audio disk for recording and reproducing audio information, besides the above described video information, as a PCM (pulse code modulated) signal, for the purpose of making use of a broad frequency band characteristic thereof. In the case of a digital audio disk, digital data representing an audio signal is modulated in a proper digital modulating system such as 8-14 modulation (eight to fourteen modulation: EFM modulation) and is then recorded on a disk. Meanwhile, by EFM modulation is meant a digital modulating system in which data of 8 bits is converted into data of 14 channel bits.
Conventionally, recording of information into and reproduction of information from such video disk, digital audio disk and the like have been made in accordance with a CAV (constant angular velocity) system for maintaining constant the rotational speed of the disk or a CLV (constant linear velocity) system for maintaining constant the relative speed (linear speed) of a disk and a pickup. According to the CAV system, the upper limit of the recording density is restricted by that in the innermost circumference of the disk, while the recording density at the outermost circumference of the disk decreases as small as several times that at the innermost circumference and accordingly the utilization efficiency of the disk area is less good. On the other hand, according to the CLV system, the relative speed (linear speed) of a disk and a pickup is made constant without regard to the outermost circumference and the innermost circumference of the disk and as a result the disk area is effectively utilized and the disk can be made compact or the amount of recorded information can be increased as compared with the CAV system. However, in the case of the CLV system, the rotational speed of a disk and thus of a motor need be continuously changed as a pickup moves from the outermost circumference to the innermost circumference or from the innermost circumference to the outermost circumference of a disk.
One example of a motor controlling apparatus for such CLV system is disclosed in Japanese Patent Laying Open No. 9907/1979 laid open Jan. 25, 1979, for example. Particularly, the referenced laying open gazette discloses an apparatus adapted for detecting the position of a pickup in the radial direction of a disk by means of a potentiometer, properly processing the output of the potentiometer to prepare a proper function and controlling the rotational speed of the motor in accordance with the function. However, the technology described in the referenced laying open gazette involves a problem that the same can not be applied to a disk of a different linear speed unless the function is changed accordingly and hence is not of versatility.
Thererfore, in order to provide such versatility, it is desired to control the rotational speed of a motor by the use of a reproduced signal from a disk. Usually a disk has information of a number of frames recorded each frame including a data synchronizing signal and data. The data synchronizing signal can be used as a signal for controlling the rotational speed of a motor in the CLV system. However, in reproducing a signal recorded in a digital modulating system of such as EFM modulation in the case of a disk of the CLV system, digital demodulation can not be made of the data synchronizing signal and the data unless a predetermined number of rotations is reached on the occasion of reproduction. Accordingly, in such a case it was extremely difficult to control with high accuracy the rotational speed of the motor by the use of a signal reproduced in a digital manner from the disk.